1. Field of the Invention
The present invention relates to an image forming apparatus, and particularly to an electrophotographic image forming apparatus such as a copier, a printer, a fax machine or a multifunction machine comprising these apparatuses.
2. Description of the Related Art
Electrophotographic image forming apparatuses conduct following process. An electrostatic latent image is formed on the surface of a photosensitive drum. Toner is then supplied onto the surface of the photosensitive drum by a developing roller of a developing device to develop the electrostatic latent image on the surface of the photosensitive drum into a toner image (development). The toner image on the photosensitive drum is transferred onto a sheet such as copy paper, plastic sheets for OHP, and the like. Finally the sheet having the toner image formed thereon is heated and pressed, as a result of which the toner image becomes fixed to the paper.
In such image forming apparatuses, as illustrated in FIG. 11, a spacer roller 103 that is concentric with the axis C1 of a developing roller 102 is mounted on both ends of the developing roller 102 along the direction in which the axis C1 of a developing roller 102 extends (at a region outside the width of a transfer member), in order to maintain a suitable gap between a photosensitive drum 101 and the developing roller 102, and to prevent occurrence of uneven development. The outer periphery of the spacer roller 103 is pushed against the outer peripheral face of the photosensitive drum 101 in such a manner that a suitable gap is maintained between the developing roller 102 and the photosensitive drum 101.
However, when toner floating in the environment around the photosensitive drum 101 and the developing roller 102 adheres to a contact region 105 of the spacer roller 103 and the photosensitive drum 101 in an image forming apparatus 104 such as the one illustrated in FIG. 11, the toner adhered is compressed by the rotating spacer roller 103 and fixed onto the outer peripheral face of the photosensitive drum 101 in the form of a ring-like toner layer. This diminishes maintaining a constant gap between the axes of the developing roller 102 and the photosensitive drum 101, and may give rise to uneven development (jitter).
To solve the above problem, an image forming apparatus 110 illustrated in FIG. 12 has mounted therein toner removing blades (blade pieces) 111 that slide against the surface of a photosensitive drum 114, for scraping the ring-like toner layer off. The toner removing blades 111 are positioned at downstream relating to a cleaning blade 113 of a cleaning device 112 in respect to a rotation direction of the photosensitive drum 114. Examples of this conventional feature are disclosed in, for instance, Japanese Patent Application Laid-open No. 1-297685.
The conventional image forming apparatus 110 illustrated in FIG. 12, however, does not accord sufficient consideration to collection of toner dust that is scraped off by the toner removing blades 111. As a result, the toner dust scraped off by the toner removing blades 111 may adhere onto the photosensitive drum 114 within an effective development width region of the latter. This may result in a new problem in that the toner dust upsets the toner image formed on the surface of the photosensitive drum 114.